carrier scanner

(Or "wardialer") A program which uses a modem to
dial a series of phone numbers (say, from 770-0000 to
770-9999), and keeps a log of what phone numbers answer with a
modem carrier. The results of such a search were generally
used by people looking to engage in random mischief in
random machines.

Since the 1980s, wardialers have generally fallen into disuse,
partly because of easily available "caller ID" technology,
partly because fax machines are now in wide use and would
often be logged as a carrier by a wardialer, and partly
because there are so many new and more interesting venues for
computerised mischief these days.